1. Field of the Invention
The present invention relates to a lens barrel, and more specifically to a lens barrel having a plurality of lens groups disposed therein so that they can extend and retract in an optical axis direction.
2. Related Art Statement
Conventionally, there are proposed various lens barrels for effecting zooming by moving frames for holding lens groups in an optical axis direction by the rotation of a cam frame accommodated inside a fixed frame.
As an example of such lens barrels, Japanese Patent Application Laid-open No. 53-102030 discloses a lens barrel provided with two fixed frames, wherein a first lens group is rotated and slid and a cam frame is driven by the rotation the  thereof to drive the other lens groups. However, the lens barrel disclosed in the publication is disadvantageous in that its structure is complex and many parts are needed and further since th e  the cam frame does not slide, an amount of movement of lenses is determined by the length of the cam frame.
Japanese Utility Model Publication No. 50-14511 discloses a lens barrel including a fixed frame, a cam frame which moves while being rotated along the cam of the fixed frame, and frames driven by the cam frame, wherein means for stopping the rotation of the frames is provided with the fixed frame. In the lens barrel disclosed in the publication, since the fixed frame is provided with a linearly traveling groove and cams for the cam frame, the disposition of the cams is regulated.
In the various kinds of proposed zoom lens barrels, when it is desired to shorten the length of the lens barrel in a retracted state to make the overall size of the lens barrel small, an amount of movement of lens groups is increased and a longer cam frame is needed accordingly.
When the length of a zoom lens barrel is shortened in a retracted state using a short cam frame as in the lens barrel disclosed in Japanese Patent Application Laid-Open No. 3-180822, two mechanisms, i.e., a mechanism for extending a lens frame unit to a certain position and a mechanism for moving the lens barrel to a finally extended position from the above position are needed, thus the arrangement of the zoom lens barrel is made complex.
When a cam frame which is long in an axis direction is used to retract lens groups whose amount of movement is increased, if the balance between the amount of movement of the lenses and the length of the cam frame is lost, the cam frame may remain projected from a lens frame although lenses are accommodated in the lens frame.
In particular, Japanese Patent Application Laid-Open No. 2-247624, for example, discloses a zoom lens barrel as an example of the lens barrels described above which is arranged such that the lens holding frames for holding lens groups are each supported by rods.
As shown, for example, in FIG. 1, such a lens barrel sequentially accommodates three lens holding frames 500b, 500c, 500d in this order from the distal end to the proximal end of an optical axis on the inner circumference of a fixed frame 500a. A rod 500e is extended from the lens holding frame 500b of these lens holding frames which is disposed on the distal side of the optical axis to the proximal side of the optical axis and inserted into bearings 500f and 500g, whereby the other lens holding frames 500c, 500d are supported movably in the optical axis direction.
In the lens barrel shown in FIG. 1, however, the rod 500e projects from the space of the lens barrel to the proximal side of the optical axis in a retracted state as shown in FIG. 2. Further, when the length of the rod is shortened to prevent its projection in the retracted state, an amount of movement of the holding frames is reduced, by which the design of the lens barrel is greatly restricted, thus, for example, it is difficult to design a zoom lens barrel having a high magnification.
In the lens barrels disclosed in Japanese Patent Application Laid-Open No. 3-39921, Japanese Patent Application Laid-Open No. 2-213813 and the like, cam grooves are defined to the above cam frame, whereas cam followers are defined to the above holding frames and the cam followers are engaged with the cam grooves of the cam frame to guide the holding frames. With respect to the disposition of the cam grooves defined to the cam frame, any one of the following arrangements is employed: bottomed cams are disposed only on any one of the inner circumference and the outer circumference of the cam frame; only passing-through cams are disposed; or a passing-through cam and a bottomed cam are disposed in combination. Further, bottomed cams are dislocated in an angular direction or in an optical axis direction from an equally divided state so that they do not cross each other.
When bottomed cams are disposed only on any of the inner circumference and the outer circumference of a cam frame as shown in the relating technologies disclosed in Japanese Patent Application Laid-Open No. 3-39921, Japanese Patent Application Laid-Open No. 2-213813 and the like, the number of cams capable of being disposed on the cam frame and the configuration of the cams are restricted, whereas when a passing-through cam and a bottomed cam are disposed in combination on the cam frame, since these two kinds of cams cannot cross each other, their design is restricted. Therefore, the diameter of the cam frame must be increased or the length thereof in an optical axis direction must be increased, by which the overall dimension of the cam frame is increased. Further, when bottomed cams are disposed so that they do not cross each other, since they must be dislocated in an angular direction or in an optical axis direction from an equally divided state, the overall dimension of the cam frame is also increased.
Further, in the lens barrel which is zoomed in such a manner that the holding frames for the lens groups are moved in an optical axis direction by the rotation of the cam frame accommodated inside the fixed frame, a rotation stop member for the lens holding frames is needed to limit the rotation of the lens holding frames which is caused by the rotation of the cam frame. Japanese Patent Application Laid-Open No. 2-201305 discloses an arrangement provided with a rotation stop member as described above and a reinforcing member for reinforcing the strength of a lens barrel, wherein a linear guide member is disposed as the rotation stop member and a guide ring is disposed as the reinforcing member and these separately provided members achieve the above respective functions. Further, a groove is defined to the frame member whose rotation is desired to be stopped and engaged with the above linear guide member to stop rotation.
When separate members are employed to stop the rotation of holding members and to reinforce the strength of a lens barrel as in the arrangement disclosed in Japanese Patent Application Laid-Open No. 2-201305, the number of parts is naturally increased and the arrangement of the frames is made complex. Further, when a groove is defined to a frame whose rotation is desired to be stopped and rotation is stopped by the engagement of the groove with a rotation stop member, the length of the rotation stop member must be at least one half an amount of movement of the frame. Thus, when the rotation of a frame having a large amount of movement is to be stopped, a longer rotation stop member is needed accordingly. As a result, the rotation stop member projects from the lens barrel in a retracted state, thus the length of the lens barrel cannot be shortened in the retracted state. Conversely, when the length of the lens barrel is shortened in the retracted state, the length of the rotation stop member is also shortened and the rotation of a frame having a large amount of movement cannot be stopped.
Incidentally, there are conventionally proposed various kinds of flexible printed substrate structures having a U-shaped bent portion so that they are accommodated in the aforesaid lens barrel.
For example, Japanese Patent Application Laid-Open No. 64-66995 discloses an example of the flexible printed substrates arranged such that a plurality of flexible printed substrates each having a U-shaped bent portion and attached to relatively moving members are accommodated in the state that the moving loci of the U-shaped bent portions are at least partially overlapped each other to thereby reduce an accommodation space.
In the structure disclosed in Japanese Patent Application Laid-Open No. 64-66995, however, when the relatively moving members are going to move, since a force for straightly extending the flexible printed substrate is applied thereto at the U-shaped portions, the force acts as a resistance to the movement of the relatively moving members. When the flexible printed substrates overlap each other at the U-shaped bent portions where the resistance occurs, the resistance is increased and there is a possibility that the above members cannot be relatively moved.
A first object of the present invention is to provide a small lens barrel.
A second object of the present invention is to provide a lens barrel whose length is shortened when it is retracted.
A third object of the present invention is to provide a lens barrel which can achieve a large amount of displacement in an optical axis direction by the smaller number of frame members.
A fourth object of the present invention is to provide a lens barrel which can achieve a large amount of displacement in an optical axis direction by the smaller number of frame members and whose length is shortened when it is retracted.
A fifth object of the present invention is to provide a lens barrel with a sufficient strength which includes lens holding frames having a large amount of movement and whose length is shortened when retracted.
A sixth object of the present invention is to provide a small lens barrel having a cam frame in which a cam groove is effectively disposed in a small space.
A seventh object of the present invention is to provide a lens barrel having a flexible printed substrate structure enabling relatively moving members to smoothly move by reducing a resistance produced at the bent portion of the flexible printed substrate.
When simply described, a lens barrel of the present invention includes a fixed frame, a plurality of lens groups disposed in the inner circumference of the fixed frame and movable along an optical axis direction with respect to the fixed frame, a lens holding frame for holding at least one of the lens groups, a cam frame coupled with the inner circumference of the fixed frame through a cam and moving along the optical axis direction with respect to the fixed frame by being rotated about an optical axis with respect to the fixed frame.
These as well as other objects and advantages of the present invention will become further apparent from the following detailed explanation.